This commit introduces the<dns> element and<txt> record for the virtual DNS
network. The DNS TXT record can be defined using following syntax in the
network XML file:
<dns>
<txt name="example" value="example value" />
</dns>
Also, the Relax-NG scheme has been altered to allow the texts without spaces
only for the name element and some nitpicks about memory free'ing have been
fixed by Laine so therefore I'm adding Laine to the SOB clause ;-)

Eww. I just realized that if you were to make one successful trip
through the loop, then hit an error on "name" the next time through,
value would still point to a string that was also pointed to by the
txtrecords array, leading to a double free during the error recovery.

To avoid this, you need to add:
name = NULL;
value = NULL;

right here. (maybe the name=NULL; value=NULL; that was in the wrong
place in the previous version of the patch used to be here, and
accidentally got moved...)